Metal/synthetic resin laminate and synthetic resin-clad metallic pipe

ABSTRACT

A metal/synthetic resin laminate comprising a metal substrate layer, an epoxy resin-based adhesive layer (a &#34;1st adhesive layer&#34;), an adhesive layer (a &#34;2nd adhesive layer&#34;) comprising an epoxidized styrenic thermoplastic elastomer D prepared through epoxidation of a double bond derived from a conjugated diene compound of a block copolymer C comprising a polymer block A composed mainly of a styrenic compound and a polymer block B composed mainly of a conjugated diene compound or a partial hydrogenation product thereof, and a synthetic resin layer; and a synthetic resin-clad metallic pipe wherein the above metal substrate layer is tubular.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the National Phase entry, under 35 USC 371, ofInternational Application PCT/JP 97/03512, filed Oct. 1, 1997.

FIELD OF THE INVENTION

The present invention relates to a metal/synthetic resin laminatewherein a synthetic resin layer is bonded to a metal substrate layer bythe mediation of an epoxy resin-based adhesive layer and an adhesivelayer formed of a specific epoxidized styrenic thermoplastic elastomerwhich are provided on the metal substrate layer, and to a syntheticresin-clad metallic pipe wherein the metal substrate layer is tubular.

BACKGROUND ART

Hitherto, coating of a metal substrate with a synthetic resin has beenpracticed in an attempt to improve corrosion resistance of the metalsubstrate. For example, a synthetic resin-clad lining pipe wherein aninner surface of the metal pipe is clad with a synthetic resin ismanufactured through the diameter-expansion method or thediameter-reduction method.

According to the diameter-expansion method, a metallic pipe and asynthetic resin pipe for cladding are provided in advance and thefollowing processes are performed: an adhesive layer is formed on theinner surface of the metallic pipe; a synthetic resin pipe for claddingis placed inside the metallic pipe; and the synthetic resin pipe forcladding is expanded by the application of heat and pressure, to therebylaminate the synthetic resin layer onto the metallic pipe via theadhesive. This method is disclosed in Japanese Patent ApplicationLaid-Open (kokai) Nos. 56-55227, 58-12720, and 59-59418.

According to the diameter-reduction method, an adhesive layer isprovided on the inner surface of a metal pipe, and a synthetic resinpipe placed inside the metallic pipe is press-laminated against themetal pipe by reduction of the diameter of the metal pipe achieved byuse of rolls, etc.

With regard to adhesives which may be used in manufacturing suchsynthetic resin-clad lining pipes, Japanese Patent Application Laid-Open(kokai) No. 56-55227 discloses a polyamide-based or polyester-basedadhesive, and Japanese Patent Application Laid-Open (kokai) No. 58-12720discloses a butadiene-styrene block copolymer elastomer-based hot-meltadhesive. There have also been used other adhesives containingpolyolefin which has been copolymerized with an unsaturated aliphaticcarboxylic acid or an anhydride thereof.

However, adhesion durability between a metal substrate and a syntheticresin for cladding is not satisfactory even when the above-mentionedadhesives are used for lamination of a synthetic resin on a metalsubstrate. Since the coefficient of linear expansion of a metalsubstrate and that of a synthetic resin for cladding significantlydiffer from each other, a metal/synthetic resin laminate easily permitsdelamination of the synthetic resin for cladding from the metallic pipeby repeated cooling-heating cycles. Similarly, delamination also occursafter repeated expansion and contraction due to changes in atmospherictemperature. Also, when adhesion between metal and synthetic resin isinsufficient, delamination tends to be caused due to application ofstress--such as bending, blanking or cutting--to thesynthetic-resin-laminated metal. Thus, improvement of adhesion between ametal substrate and a synthetic resin to be laminated is demanded.

DISCLOSURE OF THE INVENTION

The present inventors have conducted studies on adhesives for metals andsynthetic resins, and have found that laminates having excellentadhesion between the metal and the synthetic resin and durabilityagainst cooling-heating cycles are obtained through combined use of anepoxy resin adhesive and an epoxidized styrenic thermoplastic elastomer.The present invention was accomplished based on this finding.

Accordingly, the present invention provides a metal/synthetic resinlaminate comprising a metal substrate layer; an epoxy resin-basedadhesive layer (hereinafter referred to as a "1st adhesive layer"); anadhesive layer (hereinafter referred to as a "2nd adhesive layer")comprising an epoxidized styrenic thermoplastic elastomer D prepared byepoxidation of a double bond derived from a conjugated diene compound ofa block copolymer C comprising a polymer block A composed mainly of astyrenic compound and a polymer block B composed mainly of a conjugateddiene compound or a partial hydrogenation product thereof; and asynthetic resin layer. The present invention also provides ametal/synthetic resin laminate as described above, wherein the 2ndadhesive layer contains epoxidized styrenic thermoplastic elastomer D inan amount of 5-100 wt. %. The present invention further provides ametal/synthetic resin laminate as described above, wherein theepoxidation ratio of epoxidized styrenic thermoplastic elastomer Dcontained in the 2nd adhesive layer is 10-40%. The present inventionstill further provides a synthetic-resin-clad metallic pipe, wherein ametallic pipe is laminated with a 1st adhesive layer, a 2nd adhesivelayer, and a synthetic resin layer. In addition, the present inventionyet further provides a synthetic resin-clad metallic pipe as mentionedabove, wherein the inner surface of the metallic pipe is sequentiallylaminated with the above-described 1st adhesive layer, 2nd adhesivelayer, and synthetic resin layer, in this order. The present inventionwill be described in detail hereunder.

BEST MODES FOR CARRYING OUT THE INVENTION

(1) Metal/synthetic resin laminate

The metal/synthetic resin laminate of the present invention comprises ametal substrate layer, a 1st adhesive layer, a 2nd adhesive layer, and asynthetic resin layer.

(2) Metal substrate layer

As a metal substrate that serves as a constituent of the metal/syntheticresin laminate of the present invention, there may be used steel, iron,copper, aluminum, etc. formed into a sheet-like or tubular shape. Themetal substrate may have an uneven surface or may be provided withholes. The surface of the metal substrate may be subjected tosurface-treatment such as plating with zinc, chromium, etc.,phosphating, or chromating in order to enhance corrosion resistance; ordegreasing, acid-pickling, or primer-treatment with an organic compoundin order to enhance adhesion.

(3) 1st adhesive layer

The metal/synthetic resin laminate of the present invention has a 1stadhesive layer disposed on the above-described metal substrate layer.

The 1st adhesive layer is formed of an epoxy resin-based adhesive(hereinafter referred to as a "1st adhesive"), and examples of epoxyresins which may be used include a bisphenol A-type epoxy resin, abisphenol F-type epoxy resin, a novolak-type epoxy resin, and analicyclic epoxy resin. With regard to a setting agent for the epoxyresin, there may be used amine-type setting agents such as aliphatic oraromatic amines, acid anhydride-type setting agents, and cation-typesetting agents.

The 1st adhesive layer has a thickness of, preferably, 5-200 μm,particularly preferably 10-50 μm, and it may be formed on one side orboth sides of the metal substrate layer.

(4) 2nd adhesive layer

The metal/synthetic resin laminate of the present invention has a 2ndadhesive layer disposed on the 1st adhesive layer. The thickness of the2nd adhesive layer is preferably 5-500 μm, particularly preferably50-300 μm.

The adhesive that constitutes the 2nd adhesive layer (hereinafterreferred to as a "2nd adhesive") is formed of an epoxidized styrenicthermoplastic elastomer D prepared by epoxidation of a double bondderived from a conjugated diene compound of a block copolymer Ccomprising a polymer block A composed mainly of a styrenic compound anda polymer block B composed mainly of a conjugated diene compound or apartial hydrogenation product thereof.

The "styrenic compound" that constitutes the polymer block A may be oneor more species selected from among styrene, α-methylstyrene,vinyltoluene, p-tert-butylstyrene, divinylbenzene, p-methylstyrene,1,1-diphenylstyrene, vinylnaphthalene, and vinylanthracene. Of these,styrene is preferred.

The "conjugated diene compound" that constitutes the polymer block B maybe one or more species selected from among butadiene, isoprene,1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, piperylene,3-butyl-1,3-octadiene, and phenyl-1,3-butadiene. Of these, butadiene,isoprene, and combinations thereof are preferred.

The "block copolymer C" used in the present invention contains astyrenic compound structure unit in an amount of preferably 5-70 wt. %,more preferably 10-60 wt. %. The weight average molecular weight of theblock copolymer C is preferably 5,000-600,000, more preferably10,000-500,000, and the molecular weight distribution [ratio (Mw/Mn) ofweight average molecular weight (Mw) to number average molecular weight(Mn)] is preferably 10 or less. The block copolymer C preferably has alinear molecular structure. For example, a styrenic compound-conjugateddiene compound block copolymer having a structure such as A-B-A,B-A-B-A, or A-B-A-B-A is preferred. The molecule may have apolyfunctional group derived from residue of a coupling agent at an endof the molecule.

No particular limitation is imposed on the method for manufacturing theblock copolymer C so long as a polymer having the above-describedstructure is obtained. Styrenic compound-conjugated diene compound blockcopolymers may be manufactured by use of a lithium catalyst, etc. in aninert solvent in accordance with a method described in Japanese PatentPublication (kokoku) Nos. 40-23789, 43-17979, 46-32415, and 56-28925.Furthermore, partially hydrogenated block copolymers which serve asstarting materials for epoxy-modified block copolymers employed for thepresent invention may be manufactured through hydrogenation in thepresence of a hydrogenation catalyst in an inert solvent in accordancewith a method described in Japanese Patent Publication (kokoku) Nos.42-8704 and 43-6636 or Japanese Patent Application Laid-Open (kokai) No.59-133203. Degree of hydrogenation may be determined through an NMRanalysis of the block copolymers before and after hydrogenation.

In the present invention, a hydrogenation ratio is defined as thepercentage of hydrogenated double bonds with respect to the double bondsderived from a conjugated diene compound of unhydrogenated andunepoxidized, starting block copolymers. The hydrogenation ratio ispreferably 0-80%, particularly preferably 10-70%, since an epoxidizedstyrenic thermoplastic elastomer D having excellent heat resistance andcohesion characteristics is obtained within the above range.

The epoxidized styrenic thermoplastic elastomer D which may be used inthe present invention may be obtained through epoxidation of theabove-described block copolymer C. Epoxidation may be conducted throughreaction of the above-described block copolymer C with an epoxidizingagent such as hydroperoxide or peracid in an inert solvent.

In the present invention, the "inert solvent" is used in order todecrease viscosity of starting materials and dilute the epoxidizingagent to stabilize, and examples thereof which may be used includehexane, cyclohexane, toluene, benzene, ethyl acetate, carbontetrachloride, and chloroform.

Examples of the "hydroperoxides" serving as the epoxidizing agentinclude hydrogen peroxide, tertiary butyl hydroperoxide, and cumenehydroperoxide. Examples of the "peracids" include performic acid,peracetic acid, perbenzoic acid, and trifluoroperacetic acid. Of these,peracetic acid is preferred in that it is industrially manufactured on alarge scale, economically available, and has a high degree of stability.

No strict limitation is imposed on the amount of an epoxidizing agentused, and it may appropriately be selected according to species of theused epoxidizing agent, desired epoxidation degree, and differences inproperties of block copolymers used.

A "catalyst" may optionally be used at epoxidation. For example, whenperacid is used, an alkali such as sodium carbonate and an acid such assulfuric acid may be used as the catalyst, whereas when hydroperoxide isused, there may be used combinations of a tungstic acid--caustic sodamixture and hydrogen peroxide; an organic acid and hydrogen peroxide; ormolybdenum hexacarbonyl and tertiary butyl hydroperoxide to obtaincatalytic effects.

No strict limitation is imposed on the conditions of epoxidation. Forexample, the reaction temperature is preferably 0-70° C. when peraceticacid is used, since peracetic acid decomposes at temperatures greaterthan 70° C. The reaction temperature of epoxidation may be selectedaccording to a customary method depending on reactivity of theepoxidizing agent used. No particular operation is needed in relation tothe reaction mixture, and a mixture of starting materials is simplystirred for 2-10 hours.

Isolation of the resultant epoxidized styrenic thermoplastic elastomer Dmay be conducted through different methods; e.g., precipitation in apoor solvent; projection of the epoxidized styrenic thermoplasticelastomer D in hot water with stirring to remove the solvent bydistillation; or direct drying to remove the solvent by heating and/orpressure-reducing operation. In the case in which the ultimate useoccurs in the form of liquid, the solution may be used without beingsubjected to the isolation step.

The epoxidation ratio of the epoxidized styrenic thermoplastic elastomerof the present invention is defined as the percentage of epoxidizeddouble bonds with respect to the double bonds derived from a conjugateddiene compound of an unhydrogenated/unepoxidized block copolymer C, andis represented by the following equation by use of epoxy equivalent (N):Epoxidation ratio={10000×D+2×H×(100-S)}/{(N-16)×(100-S)} wherein Drepresents the molecular weight of diene compound; H represents thehydrogenation ratio (%); and S represents the styrenic compoundcontent(wt. %).

In the present invention, the epoxy equivalent (N) of epoxidizedstyrenic thermoplastic elastomer D is obtained through titration with0.1 N solution of hydrobromic acid and may be represented by thefollowing equation:

    Epoxy equivalent (N)=10000×W/(f×V)

wherein W represents the weight of the epoxidized styrenic thermoplasticelastomer to be titrated; V represents consumption of the solution ofhydrobromic acid in milli milliliter at titration; and f represents thefactor of the solution of hydrobromic acid.

The epoxidized styrenic thermoplastic elastomer D of the presentinvention has an epoxidation ratio of preferably 10-40%, particularlypreferably 15-35%. When the ratio is less than 10%, the effect of thepresent invention is not satisfactory, whereas when it is in excess of40%, reactivity attributed to epoxy groups increases considerably toresult in easy gelling and low thermal stability.

In the case in which thermal stability is strongly sought, thepercentage of bonds remaining unsaturated, which are derived from aconjugated diene compound subjected to neither hydrogenation norepoxidation, is preferably less than 90% of the entirety, with 40% orless being particularly preferred.

In the present invention, the 2nd adhesive contains epoxidized styrenicthermoplastic elastomer D in an amount of preferably 5-100 wt. %,particularly preferably 20-100 wt. %, since satisfactory adhesion isobtained within the above range.

Examples of other components which may be incorporated into the 2ndadhesive are as follows.

1) Examples of thermoplastic resins include polyolefin-based resins,polyamide-based resins, polyester-based resins, terpene-phenolic resins,and alicyclic saturated hydrocarbon resins. These thermoplastic resinsmay be incorporated into the 2nd adhesive in amounts of 0-80 wt. %.

2) Examples of thermosetting resins which may be incorporated into anadhesive used for metal-vinyl chloride-based resins include epoxy-basedresins, phenol-based resins, urea-based resins, and melamine-basedresins. These thermosetting resins may be incorporated into the 2ndadhesive in amounts of 0-80 wt. %.

3) Examples of resin tackifiers which may be incorporated include rosin,terpene-based resins, aliphatic hydrocarbon resins, aromatic hydrocarbonresins, phenol-based resins, and cumarone-indene-based resins. Theseresin tackifiers may be incorporated into the 2nd adhesive in amounts of0-80 wt. %.

4) Examples of inorganic fillers which may be incorporated includecalcium carbonate barium sulfate, silica, talc, clay, titanium oxide,magnesium carbonate, and carbon black. These may be incorporated intothe 2nd adhesive in amounts of 0-60 wt. %.

5) Examples of fluidity-modifiers which may be incorporated includenaphthene-based, aroma, and paraffin-based oil. These may beincorporated into the 2nd adhesive in amounts of 0-60 wt. %.

6) Examples of plasticizers which may be incorporated include dioctylphthalate (DOP) and dibutyl phthalate (DBP). These may be incorporatedinto the 2nd adhesive in amounts of 0-60 wt. %.

7) Other than the above-described components, stabilizers such asanti-oxidants and UV-absorbers; colorants; pigments; may be added.

Examples of methods for manufacturing the 2nd adhesive includemelt-mixing of the epoxidized styrenic thermoplastic elastomer D andoptional components; or dissolving the epoxidized styrenic thermoplasticelastomer D in a solvent and mixing other components. These componentsare typically mixed with a kneader, a seal-type kneader, an extruder, amixing roll, a Banbury mixer, etc. with the application of heat in anoptional inert gas atmosphere.

(5) Synthetic resin layer

Examples of synthetic resins that constitute metal/synthetic resinlaminates of the present invention include vinyl chloride-based resins,olefin-based resins, polyester-based resins, and polyamide-based resins.Of these, vinyl chloride-based resins are particularly preferred.

When vinyl chloride-based resins are used as the synthetic resins, theremay be used one or more species selected from among vinyl chlorideresins; copolymers of a vinyl chloride monomer and monomerscopolymerizable with the vinyl chloride monomer; and post-chlorinatedvinyl chloride-based resins obtained through post-chlorination of avinyl chloride resin. Examples of the copolymers of a vinyl chloridemonomer and monomers copolymerizable with the vinyl chloride monomerinclude vinyl chloride-styrene copolymers, vinyl chloride-ethylenecopolymers, and vinyl chloride-ethylene-vinyl acetate copolymers.

The metal/synthetic resin laminate of the present invention comprises ametal substrate layer (M layer), a 1st adhesive layer (B1 layer), a 2ndadhesive layer (B2 layer), and a synthetic resin layer (P layer) with astructure of M layer-B1 layer-B2 layer-P layer. The present inventionalso encompasses a laminate comprising a metal substrate layer of whichboth surfaces are sequentially laminated with B1 layers, B2 layers, andP layers, i.e., a laminate of a 7-layer structure (P layer-B2 layer-B1layer-M layer-B1 layer-B2 layer-P layer).

The 1st adhesive used in the metal/synthetic resin laminate of thepresent invention exhibits excellent adhesion to metals and affinitywith the epoxidized styrenic thermoplastic elastomer D used as the 2ndadhesive. The 2nd adhesive also has excellent adhesion to syntheticresins. Consequently, each of the layers in the obtained metal/syntheticresin laminate exhibits strong adhesion to its adjacent layers. Sincethe 2nd adhesive layer has appropriate elasticity, the layer absorbscontraction stress attributed to difference between linear expansioncoefficients of the synthetic resin and the metal substrate, even atevaluation of durability such as a cooling-heating cycle test, toreinforce adhesion between the metal substrate and the synthetic resinexhibiting a large difference in linear expansion coefficient.

The metal/synthetic resin laminate of the present invention ismanufactured in accordance with a known method, e.g., application of the1st adhesive and the 2nd adhesive in the form of solution on a metalsheet subjected to pretreatment such as degreasing; drying to form eachof the adhesive layers; and pressing with a synthetic resin sheet underheat.

(6) Synthetic resin-clad metallic pipe

The synthetic resin-clad metallic pipe of the present inventioncomprises a metallic pipe sequentially laminated with a 1st adhesivelayer (B1 layer), a 2nd adhesive layer (B2 layer), and a synthetic resinlayer (P layer) in this order. The inner surface of the metallic pipemay be sequentially laminated with B1 layer-B2 layer-P layer in thisorder. The present invention also includes a laminate comprising ametallic pipe (M layer) of which both surfaces are sequentiallylaminated with B1 layers, B2 layers, and P layers in this order, i.e., alaminate of a 7-layer structure (P layer-B2 layer-B1 layer-M layer-B1layer-B2 layer-P layer).

The synthetic resin-clad metallic pipe of the present invention may bemanufactured through a diameter-expansion method including the steps ofapplying the 2nd adhesive at first and then the 1st adhesive in the formof solution onto the outer surface of a synthetic resin pipe, drying toform each of the adhesive layers, insertion of the resin pipe into themetallic pipe, and heating or pressurizing the resin pipe; or through adiameter-reduction method, etc.

The synthetic resin-clad metallic pipe of the present inventioneffectively prevents corrosion of the metallic pipe, due to strongadhesion of the synthetic resin layer. When the pipe is used as a liningpipe disposed at a place where a large temperature difference ispresent, the pipe also prevents delamination of the clad resin layerinduced by the temperature difference.

EXAMPLES

The present invention will next be described in detail by way ofexamples, which should not be construed as limiting the invention. Asused herein, "%" means "wt. %" unless otherwise indicated.

Manufacture Example 1

A linear polystyrene-polybutadiene-polystyrene block copolymer("TR2000," styrene content 40%, product of Japan Synthetic Rubber Co.,Ltd.) (300 g) and ethyl acetate (1,500 g) were placed in a reactorhaving a jacket and equipped with a stirrer, a reflux condenser, and athermometer, and the mixture was allowed to dissolve. An ethyl acetatesolution (169 g) containing 30% peracetic acid was then continuouslyadded dropwise thereto, and the mixture was allowed to react for threehours under stirring to cause epoxidation at 40° C. The reaction mixturewas cooled to ambient temperature and removed from the reactor. A largeamount of methanol was added thereto to precipitate a polymer, which wasseparated, washed with water, and dried to thereby obtain an epoxidizedstyrenic thermoplastic elastomer (elastomer A) having an epoxyequivalent of 470 (epoxidation ratio=19%).

Manufacture Example 2

A linear polystyrene-polybutadiene-polystyrene block copolymer("TR2000," styrene content 40%, product of Japan Synthetic Rubber Co.,Ltd.) (300 g) and cyclohexane (3,000 g) were placed in a reactor havinga jacket and equipped with a stirrer and a thermometer, and the mixturewas allowed to dissolve. Adi-p-tolylbis(1-cyclopentadienyl)titanium/cyclohexane solution(concentration 1 mmol/l) (40 ml) and an n-butyllithium solution(concentration 5 mmol/l) (8 ml) were mixed at 0° C. under hydrogen at apressure of 2.0 kg/cm² to obtain a hydrogenation catalyst. The catalystwas added to the mixture and the resultant mixture was allowed to reactat the partial pressure of hydrogen of 2.5 kg/cm2 for 30 minutes.

The obtained solution of a partial hydrogenation polymer was dried underreduced pressure to remove the solvent (hydrogenation ratio of totaldouble bonds derived from butadiene: 30%). The partial hydrogenationpolymer (300 g) and cyclohexane (1500 g) were placed in a reactor havinga jacket and equipped with a stirrer, a reflux condenser, and athermometer, and the mixture was allowed to dissolve. An ethyl acetatesolution (300 g) containing 30% of peracetic acid was then continuouslyadded dropwise thereto, and the mixture was allowed to react for threehours under stirring to cause epoxidation at 40° C. The reaction mixturewas cooled to ambient temperature and removed from the reactor. A largeamount of methanol was added thereto to precipitate a polymer, which wasseparated, washed with water, and dried to thereby obtain an epoxidizedstyrenic thermoplastic elastomer (elastomer B) having an epoxyequivalent of 275 (epoxidation ratio=33.6%).

Example 1

As the 1st adhesive, an epoxy resin and a setting agent were dissolvedto form a composition specified in Table 1 in toluene so that the solidcontent thereof became 50 wt. %. As the 2nd adhesive, the elastomer Aobtained through Manufacture Example 1 and a tackifier specified inTable 1 were dissolved in toluene so that the solid content thereofbecame 50 wt. %.

Next, a cold-rolled steel (JIS G3141) sheet of 25 mm×125 mm×1.6 mm(thickness) was surface-degreased with methanol and an area thereof (25mm×60 mm) was sequentially coated with a 1st adhesive and 2nd adhesivein this order to a thickness of 50 μm and 150 μm, respectively, and theadhesives were dried. The sheet was laminated with a flexible vinylchloride (chlorinated vinyl chloride) sheet of 25 mm×180 mm×0.5 mm(thickness) and the laminate was pressed at 150° C. for five minuteswith a pressure of 2 kgf/cm², to thereby obtain a metal/synthetic resinlaminate. The 180 degree peeling strength and shear strength of thesheet were measured and the results are shown in Table 1.

The 2nd adhesive and 1st adhesive prepared above were applied, in thisorder, to the outer surface of a chlorinated vinyl chloride sheetsynthetic resin pipe having an outside diameter of 49 mm so that thethicknesses became 150 μm and 50 μm, respectively, and were dried. Theresin pipe was inserted into a steel pipe having an inside diameter of50 mm and the synthetic resin pipe was heated at 150-190° C. andpressurized to thereby obtain a synthetic resin-clad metallic pipe,which was subjected to a cooling-heating cycle test. The results areshown in Table 1.

Examples 2 through 5

The procedure of Example 1 was performed through use of 1st adhesivesand 2nd adhesives shown in Table 1, to thereby obtain metal/syntheticresin laminates and synthetic resin-clad metallic pipes. The 180 degreepeeling strength and tensile shear strength thereof were measured, and acooling-heating cycle test was performed in the manner described inExample 1. The results are shown in Tables 1 and 2.

Comparative Example 1

The procedure of Example 1 was performed through use of an unepoxidizedstyrenic elastomer C as the 2nd adhesive, to thereby obtain ametal/synthetic resin laminate and a synthetic resin-clad metallic pipe.The 180 degree peeling strength and tensile shear strength thereof weremeasured, and a cooling-heating cycle test was performed in the mannerdescribed in Example 1. The results are shown in Table 2. The resultsshow that poor adhesion was obtained after the cooling-heating cycletest, due to low 180 degree peeling strength and tensile shear strengtheven though the 2nd adhesive layer had appropriate elasticity.

Comparative Example 2

The procedure of Example 1 was performed through exclusive use of the2nd adhesive layer for adhesion without use of a 1st adhesive, tothereby obtain a metal/synthetic resin laminate and a syntheticresin-clad metallic pipe. The 180 degree peeling strength and tensileshear strength were measured, and a cooling-heating cycle test wasperformed in the manner described in Example 1. The results are shown inTable 2. The results show that poor adhesion was obtained after thecooling-heating cycle test, due to low tensile shear strength eventhough the 2nd adhesive layer had appropriate elasticity.

Comparative Example 3

The procedure of Example 1 was performed through exclusive use of the1st adhesive layer for adhesion without use of a 2nd adhesive layer, tothereby obtain a metal/synthetic resin laminate and a syntheticresin-clad metallic pipe. The 180 degree peeling strength and tensileshear strength were measured, and a cooling-heating cycle test wasperformed in the manner described in Example 1. The results are shown inTable 2. As shown in the results, poor adhesion was obtained after thecooling-heating cycle test, since contraction stress attributed todifference between linear expansion coefficients was absorbed due to theabsence of the 2nd adhesive layer having appropriate elasticity.

                                      TABLE 1                                     __________________________________________________________________________                          Example 1                                                                           Example 2                                                                           Example 3                                                                           Example 4                             __________________________________________________________________________    Steel sheet or steel pipe serving as a metal                                                        Degreasing                                                                          Degreasing                                                                          Degreasing                                                                          Degreasing                            substrate             treatment                                                                           treatment                                                                           treatment                                                                           treatment                             Composition of 1st adhesive layer (parts by weight)                           Epikote 1001*.sup.1   100   100   100   100                                   DICY*.sup.2           6                                                       TMA*.sup.3                  16                                                TETA*.sup.4                       6                                           2nd adhesive layer    50    50    50                                          Styrene elastomer A                     50                                    Styrene elastomer B   50    50    50    50                                    YS Polystar T145*.sup.6                                                       Harimac T80*.sup.7                                                            Evaluation of adhesion strength                                               180 Deg. peeling strength (kgf/25 mm)                                                               >5.7  >5.3  >5.5  >5.6                                  Tensile shear strength (kgf/25 mm.sup.2)                                                            56.8  47.8  59.8  57.1                                  Cycle test                                                                    State of initial adhesion                                                                           ∘                                                                       ∘                                                                       ∘                                                                       ∘                         After 70 coolong/heating cycles                                                                     ∘                                                                       ∘                                                                       ∘                                                                       ∘                         __________________________________________________________________________     *1: Epoxy resin; bisphenol Atype epoxy resin, product of Yuka Shell Epoxy     Co., Ltd.                                                                     *2: Setting agent; "dicyanediamide"-                                          *3: Setting agent; "trimellitic acid"-                                        *4: Setting agent; "triethylenetetramine"-                                    *6: Tackifier; terpenephenolic resin, product of Yasuhara Chemical, Co.,      Ltd.                                                                          *7: Tackifier; rosinmodified maleic acid resin "Harimac T80," product of      Harima Chemicals, Inc.                                                   

                                      TABLE 2                                     __________________________________________________________________________                          Example 5                                                                           Com. Ex. 1                                                                          Com. Ex. 2                                                                          Com. Ex. 3                            __________________________________________________________________________    Steel sheet serving as a metal substrate                                                            Degreasing                                                                          Degreasing                                                                          Degreasing                                                                          Degreasing                                                  treatment                                                                           treatment                                                                           treatment                                                                           treatment                             Composition of 1st adhesive layer (parts by weight)                           Epikote 1001*.sup.1   100   100         100                                   DICY*.sup.2           6     6           6                                     2nd adhesive layer    50          50                                          Styrene elastomer A         50                                                Styrene elastomer C*.sup.5  50    50                                          YS Polystar T145*.sup.6                                                                             50                                                      Harimac T80*.sup.7                                                            Evaluation of adhesion strength                                               180 Deg. peeling strength (kgf/25 mm)                                                               >5.7  1.4   >5.3  0.2                                   Tensile shear strength (kgf/25 mm.sup.2)                                                            48.2  28.2  34.1  81.4                                  Cycle test                                                                    State of initial adhesion                                                                           ∘                                                                       ∘                                                                       ∘                                                                       ∘                         After 70 coolong/heating cycles                                                                     ∘                                                                       Δ                                                                             Δ                                                                             X                                     __________________________________________________________________________     *1: Epoxy resin; bisphenol Atype epoxy resin, product of Yuka Shell Epoxy     Co., Ltd.                                                                     *2: Setting agent; "dicyanediamide"-                                          *5: "TR 2000," styrene content 40%, product of Japan Synthetic Rubber Co.     Ltd.                                                                          *6: Tackifier; terpenephenolic resin, product of Yasuhara Chemical, Co.,      Ltd.                                                                          *7: Tackifier; rosinmodified maleic acid resin "Harimac T80," product of      Harima Chemicals, Inc.                                                   

(Evaluation tests)

(1) 180 Degree peeling test

The synthetic resin layer of a metal/synthetic resin laminate was cut onthree sides of a 25 mm×250 mm square and the square was peeled at anangle of 180° to the sheet at the peeling rate of 100 mm/minute and 23°C. The unit of peeling strength is kgf/mm.

(2) Tensile shear test

The test was conducted for a metal/synthetic resin laminate with atensile speed of 10 mm/minute at 23° C., to thereby measure the shearstrength.

(3) Cooling-heating cycle test

Initial adhesion of a synthetic resin-clad metallic pipe was evaluatedby visual observation. The pipe was subjected to 70 cooling-heatingcycles, i.e., dipping for 5 minutes in cold water at 23° C. and dippingfor 5 minutes in hot water at 85° C., then the adhesion state wasevaluated by visual observation. Evaluation is categorized as follows:

◯: State where no delamination was observed between the metallic pipeand chlorinated vinyl chloride material.

Δ: State where partial delamination was observed between the metallicpipe and chlorinated vinyl chloride material.

×: State where apparent delamination was observed between the metallicpipe and chlorinated vinyl chloride material.

Industrial Applicability

The present invention provides a metal/synthetic resin laminate havingexcellent adhesion, wherein adhesion between the metal substrate and thesynthetic resin layer is achieved through combination of two specificadhesives. Since the 1st adhesive is an epoxy resin-based adhesiveexhibiting excellent adhesion both to the metal substrate and the 2ndadhesive, a metal/synthetic resin laminate exhibiting high adhesionstrength to metal substrates can be obtained. Moreover, the 2nd adhesiveabsorbs strain attributed to difference between linear expansioncoefficient of a synthetic resin and that of a metal effectively,because it contains as the primary component an epoxidized styrenicthermoplastic elastomer having a specific structure. Therefore, theremay be obtained metal/synthetic resin laminates and synthetic resin-cladmetallic pipes exhibiting excellent durability in, for example,cooling-heating cycle tests.

What is claimed is:
 1. A metal/synthetic resin laminate comprising ametal substrate layer; an epoxy resin-based adhesive layer (a "1stadhesive layer"); an adhesive layer (a "2nd adhesive layer") comprisingan epoxidized styrenic thermoplastic elastomer D prepared by epoxidationof a double bond derived from a conjugated diene compound of a blockcopolymer C comprising a polymer block A composed mainly of a styreniccompound and a polymer block B composed mainly of a conjugated dienecompound or a partial hydrogenation product thereof; and a syntheticresin layer;wherein said 1st adhesive layer is adherent to the metalsubstrate layer and has affinity with the thermoplastic elastomer D ofthe 2nd adhesive layer and said second adhesive layer, which isdifferent than the 1st adhesive layer, is adherent to the syntheticresin layer and provides elasticity to absorb contraction stressresulting from differences in linear expansion coefficients of thesynthetic resin and the metal substrate.
 2. The metal/synthetic resinlaminate according to claim 1, wherein the 2nd adhesive layer comprisesan adhesive containing the epoxidized styrenic thermoplastic elastomer Din an amount of 5-100 wt. %.
 3. The metal/synthetic resin laminateaccording to claim 1 or 2, wherein the epoxidation ratio of theepoxidized styrenic thermoplastic elastomer D contained in the 2ndadhesive layer is 10-40%.
 4. A synthetic-resin-clad metallic pipe,wherein a metallic pipe is laminated with an epoxy resin-based adhesivelayer (a "1st adhesive layer"); an adhesive layer (a "2nd adhesivelayer") comprising an epoxidized styrenic thermoplastic elastomer Dprepared by epoxidation of a double bond derived from a conjugated dienecompound of a block copolymer C comprising a polymer block A composedmainly of a styrenic compound and a polymer block B composed mainly of aconjugated diene compound or a partial hydrogenation product thereof;and a synthetic resin layer;wherein said 1st adhesive layer is adherentto the metallic pipe and has affinity with the thermoplastic elastomer Dof the 2nd adhesive layer and said second adhesive layer, which isdifferent than the 1st adhesive layer, is adherent to the syntheticresin layer and provides elasticity to absorb contraction stressresulting from differences in linear expansion coefficients of thesynthetic resin and the metal substrate.
 5. The synthetic-resin-cladmetallic pipe according to claim 4, wherein the inner surface of themetallic pipe is sequentially laminated with an epoxy resin-basedadhesive layer (a "1st adhesive layer"); an adhesive layer (a "2ndadhesive layer") comprising an epoxidized styrenic thermoplasticelastomer D prepared by epoxidation of a double bond derived from aconjugated diene compound of a block copolymer C comprising a polymerblock A composed mainly of a styrenic compound and a polymer block Bcomposed mainly of a conjugated diene compound or a partialhydrogenation product thereof; and a synthetic resin layer, in thisorder.
 6. The metal/synthetic resin laminate according to claim 1 orclaim 2, wherein the 1st adhesive layer comprises an epoxy resinselected from the group consisting of bisphenol A epoxy resins,bisphenol F epoxy resins, novolak epoxy resins and alicyclic epoxyresins.
 7. The metal/synthetic resin laminate according to claim 6,wherein the 1st adhesive layer further comprises a setting agent for theepoxy resin, said setting agent being selected from the group consistingof amine setting agents, acid anhydride setting agents and cationsetting agents.
 8. The metal/synthetic resin laminate according to claim7, wherein the epoxidation ratio of the epoxidized styrenicthermoplastic elastomer D contained in the 2nd adhesive layer is from 10to 40%.
 9. The metal/synthetic resin laminate according to claim 8,wherein the epoxidation ratio is from 15 to 35%.
 10. The metal/syntheticresin laminate according to claim 1, wherein the 1st adhesive layer hasa thickness of from 5 to 200 μm and the 2nd adhesive layer has athickness of from 5 to 500 μm.
 11. The metal/synthetic resin laminateaccording to claim 1, wherein the 1st adhesive layer has a thickness offrom 10 to 50 μm and the 2nd adhesive layer has a thickness of from 50to 300 μm.
 12. The metal/synthetic resin laminate according to claim 1,comprising a seven layer structure comprising synthetic resin layer/2ndadhesive layer/1st adhesive layer/metal layer/1st adhesive layer/2ndadhesive layer/synthetic resin layer.
 13. The metal/synthetic resinlaminate according to claim 1, wherein the percentage of conjugateddouble bonds in polymer block B, based on the total of conjugated doublebonds, hydrogenated double bonds and epoxidized double bonds is lessthan 40%.
 14. The metal/synthetic resin laminate according to claim 1,wherein the synthetic resin layer comprises olefin resin, polyesterresin or polyamide resin.
 15. The metal/synthetic resin laminateaccording to claim 1, wherein the synthetic resin layer comprises vinylchloride resin.
 16. The synthetic-resin-clad metallic pipe according toclaim 4 or claim 5, wherein the 1st adhesive layer comprises an epoxyresin selected from the group consisting of bisphenol A epoxy resins,bisphenol F epoxy resins, novolak epoxy resins and alicyclic epoxyresins.
 17. The synthetic-resin-clad metallic pipe according to claim16, wherein the 1st adhesive layer further comprises a setting agent forthe epoxy resin, said setting agent being selected from the groupconsisting of amine setting agents, acid anhydride setting agents andcation setting agents.
 18. The synthetic-resin-clad metallic pipeaccording to claim 17, wherein the epoxidation ratio of the epoxidizedstyrenic thermoplastic elastomer D contained in the 2nd adhesive layeris from 10 to 40%.
 19. The synthetic-resin-clad metallic pipe accordingto claim 18, wherein the epoxidation ratio is from 15 to 35%.
 20. Thesynthetic-resin-clad metallic pipe according to claim 4 or claim 5,wherein the 1st adhesive layer has a thickness of from 5 to 200 μm andthe 2nd adhesive layer has a thickness of from 5 to 500 μm.
 21. Thesynthetic-resin-clad metallic pipe according to claim 4 or claim 5,wherein the 1st adhesive layer has a thickness of from 10 to 50 μm andthe 2nd adhesive layer has a thickness of from 50 to 300 μm.
 22. Thesynthetic-resin-clad metallic pipe according to claim 4, comprising aseven layer structure comprising synthetic resin layer/2nd adhesivelayer/1st adhesive layer/metal pipe/1st adhesive layer/2nd adhesivelayer/synthetic resin layer.
 23. The synthetic-resin-clad metallic pipeaccording to claim 4 or claim 5, wherein the percentage of conjugateddouble bonds in polymer block B, based on the total of conjugated doublebonds, hydrogenated double bonds and epoxidized double bonds is lessthan 40%.
 24. The metal/synthetic resin laminate according to claim 4 orclaim 5, wherein the synthetic resin layer comprises vinyl chlorideresin, olefin resin, polyester resin or polyamide resin.